Thermosetting coating compositions containing one or more thermosettable polyesters, an aminoplast resin crosslinking agent and a curing catalyst consisting of a strong acid are well known. Such prior art compositions may be used as printing inks by incorporating pigments and appropriate solvents therein. It has now been found that if a functional, i.e. reactive, copolymer of a thermosettable polyester and a type of polysiloxane is used instead of the polyester, the resultant ink composition possesses improved pigment wetting, reduced initial shear viscosity, lower contact angle and lower surface tension. The printing ink compositions of the present invention also exhibited improved transfer and laydown, higher gloss and increased color strength.
U.S. Pat. No. 4,370,441 discloses a coating composition containing three components: an essentially nonfunctional organic solvent-soluble silicone resin reaction product of a highly branched, low molecular weight hydroxy-functional polyester with an hydroxy or alkoxy-functional polysiloxane; a second component consisting of an organic solvent-soluble, essentially linear, low molecular weight, hydroxy-functional polyester and a heterocyclic aminoplast resin for curing the second component.
The compositions of the aforesaid '441 patent are prepared such that, upon curing, no significant combination of the nonfunctional polyester-silicone reaction product with either the reactive polyester or the aminoplast resin will occur, i.e. stratification of the coating will occur and the silicone will rise to the coating surface to provide the desired weather resistance. In contrast thereto, the compositions of the present invention are prepared such that the polyester-silicone copolymer is functional, i.e. reactive in nature, and such copolymer will combine with the crosslinking agent.